Rapid thermal processing systems are being increasingly used for microelectronic device fabrication. As is well known to those having skill in the art, rapid thermal processing systems attain a desired processing temperature rapidly, without the need for a lengthy "ramp-up" period. It has been found that rapid thermal processing systems allow microelectronic devices to be fabricated at high temperatures without causing dopant diffusion or other unwanted side effects. Since rapid thermal processing systems typically process semiconductor wafers, the term "wafer" will be used herein to designate any device processed in the rapid thermal processing system. It will be understood by those having skill in the art that other substrates or materials may be processed.
In contrast with a conventional furnace which typically uses resistive heating units, a rapid thermal processing system typically uses radiant heat sources, for example, arc lamps or tungsten-halogen lamps. A small processing chamber is typically used, to provide a controlled environment for the wafer to be processed and to efficiently couple the heat energy from the radiant energy sources to the wafer. Rapid thermal processing systems have heretofore been used for rapid thermal annealing and rapid thermal oxidation of semiconductor wafers. More recently, rapid thermal processing systems have also been used in rapid thermal chemical vapor deposition processes.
Two major design considerations in a rapid thermal processing system are heating efficiency and temperature uniformity. Efficient coupling of the radiant heat from the lamps to the wafer is necessary so that large increases in wafer temperature can be produced in a short time. Moreover, in producing the rapid increase in wafer temperature, a uniform temperature distribution must be provided across the face of the wafer. Lack of uniformity can produce excessive microelectronic device variation across the face of the wafer or may render the wafer unusable because of internal crystalline dislocations or even wafer cracking.
Conventional rapid thermal processing systems use a cylindrical quartz tube as a thermal processing chamber, with a wafer holder for holding the wafer face transverse to the axis to the tube. One or more lamps is placed above and/or below the wafer, to radiate onto the face of the wafer. See, for example, U.S. Pat. No. 4,481,406 to Muka entitled Heater Assembly for Thermal Processing of a Semiconductor Wafer in a Vacuum Chamber; U.S. Pat. No. 4,560,420 to Lord entitled Method for Reducing Temperature Variations Across a Semiconductor Wafer During Heating, and U.S. Pat. No. 4,818,327 to Davis et al. entitled Wafer Processing Apparatus.
Rapid thermal processing system with lamps above and/or below the face of the wafer can efficiently couple radiant energy from the lamps to the wafer face. Unfortunately, poor thermal uniformity across the face of the wafer is often present.
Recently, a rapid thermal processing system has been proposed, in which an array of lamps extend in a cylinder around the edge of the wafer. See a publication entitled A Cylindrical Tube Based Rapid Thermal Processor by D. T. Chapman et al., including the present inventors, Extended Abstracts of the 179th Electrochemical Society Meeting, No. 358, pp. 541, May 1991, the disclosure of which is hereby incorporated herein by reference. Unfortunately, although this design results in improved temperature uniformity, coupling efficiency between the radiant sources and the wafer is low. Therefore, this configuration may not produce as high a wafer temperature, or as rapid a temperature increase, as is desirable.